Optical trapping provides a tool for the manipulation of small objects between nanometer and micrometer scales. By trapping or moving the small objects, such tools are capable of, e.g., applying measurable forces to dielectric particles. In other experiments, optical forces are applied to a polystyrene microsphere bead attached to a protein of interest. The microsphere is trappable and provides a convenient handle to manipulate the protein so as to make quantitative measurements of mechanical properties in connection with the spatial manipulation of biological polymers as well as the force generation mechanisms of molecular motors.
Recently, attempts at using a multicore fibers (MCF) for optical trapping have been made. An MCF typically has several cores surrounded in one buffer coating, and independent beams can be transmitted through each of the cores. Attempts to employ MCF for optical trapping have entailed micromachining (e.g., mirror milling and lens shaping) techniques for modifying ends of the cores to enable them to emit beams establishing an optical trap. Absent free space optics, however, such beams from a single fiber-coupled laser source are not movable relative to each other. Furthermore, separate (expensive) laser sources may provide separate beams, but these are difficult to set-up and properly align and there are problems such as optical loss and diffraction stemming from such techniques.
Similarly, currently available laser systems capable of varying beam characteristics use free-space optics or other complex and expensive add-on mechanisms (e.g., zoom lenses, mirrors, translatable or motorized lenses, combiners, etc.) in order to vary beam characteristics. No solution exists that provides the desired adjustability in beam characteristics (i.e., spatial distribution) that minimizes or eliminates reliance on the use of free-space optics or other extra components that add significant penalties in terms of cost, complexity, performance, and/or reliability. What is needed is an in-fiber apparatus for providing varying beam characteristics so as to manipulate distributions of light selected to travel through one or more selectable cores of an MCF-coupled optical probe device.